The Ephel Dúath, or the Mountains of Shadow, were a range of mountains that guarded Mordor's western and southern borders.

Geography

The mountain range met the Ered Lithui at the Morannon, so that between them the mountain ranges effectively seal off Mordor from invasion on three sides.

There were only two known passes through them: the "Nameless Pass" that ran between Minas Morgul and Mordor, and the nearby Pass of Cirith Ungol. The Morannon was the only pass through Mordor's outer mountain chains through which large armies could easily pass, but apparently small amounts of troops were able to slowly funnel through the Nameless Pass. However, the Pass of Cirith Ungol was extremely inaccessible, involving climbing up or down the section called the Straight Stair, making it practically impossible to for easy travel of large numbers of troops, much less horses and wagons.